This invention relates generally to a method and apparatus for measuring the temperature of an external medium or approximate body, and particularly a moving external body.
The temperature of moving and non-moving objects is generally now measured by a variety of methods and apparatuses including non-contact temperature detection devices which rely on the principle that net heat exchange between a reference body and an external body is zero when the bodies are at the same temperature. Reference is made to U.S. Pat. Nos. 3,542,123 and 3,715,923 for details regarding an apparatus employing this principle. Such non-contact devices contain a high thermal conductivity reference body mounting a heat flow sensor to determine the heat flow between the reference body and an external body located adjacent to the reference body. A temperature sensor provides a signal proportional to the temperature of the referenced body. In addition, the apparatus includes means for establishing the spacing between the reference and external bodies so that the heat flow sensor output signal can be calibrated to yield the absolute temperature of the external body.
As the external body moves past the heat flow sensitive surface of the reference body, heat will be exchanged by convection between the external and reference bodies whenever they are not at the same temperature. This will cause heat to flow into or out of the sensing head surface of the reference body. The magnitude of heat flow will be proportional to the temperature difference between the bodies, the distance between the bodies, and the thermal conductance of the heat flow path across the spacing between them. By keeping the spacing constant, it is possible to calibrate the heat flow rate, measured by the heat flow sensor in the reference body, as a function of the temperature difference between the reference and external bodies for a given reference body temperature. By adding this measured, calibrated temperature difference between the bodies to the reference body temperature measured by the temperature sensor in the reference body, the temperature of the external moving body is obtained. While the devices are primarily used to measure the temperature of moving objects, they are suitable for many applications involving stationary objects as well.
However, one major drawback of these non-contact devices is that they must be manually recalibrated whenever the spacing or heat transfer conditions between the reference and external bodies changes, thereby resulting in unnecessary delays.
Therefore, it is a primary object of the present invention to provide an improved, convenient method and apparatus for measuring the temperature of an external body that continues to function even as conditions between the apparatus and external body change.
It is another object of the present invention to provide an improved method and apparatus for measuring the temperature of an external body that automatically calculates the proportionality constant between the heat flow rate and the temperature gradient between the external body and the reference body.
It is a further object of the present invention to provide an improved method and apparatus for measuring the temperature of fast-moving continuous elements such as wires, filaments, webs and rolls.